1. Field of the Invention
This invention relates to record players, i.e., to equipment useful with a phonograph record disc to sense by a stylus, and to convert by a transducer to an electrical signal, audio information contained in the contours of the spiral groove defined in the disc. More particularly, it relates to a programmable record player in which the stylus moves across a record disc along a line radially of the disc axis of rotation and in which the transducer cartridge, to which the stylus is mounted, is carried in a novel suspension which enables substantially zero tracking force to be achieved between the stylus and the record disc and which, apart from the overall radial-tracking movement, constrains the cartridge to move without change in the tracking force only perpendicular to the disc's plane of rotation under loads imposed on the stylus by the record.
2. Review of the Prior Art
My prior U.S. Pat. No. 3,658,347 describes a record player in which a phonograph record disc, during playing of the record when a stylus is engaged in the record's spiral groove, is held captive between a driven record supporting turntable below the record and a clamp disc above the record. The stylus is carried by a transducer cartridge which is mounted in a carriage located above the record. The carriage is supported on rollers engaged in rails so disposed that the path of movement of the stylus, overall across the record, is along a line parallel to and radially of the record.
The advantages of radial-tracking record players, as compared to record players in which the stylus and the cartridge are mounted on the end of a long pivoted tone arm, is that the stylus path of movement across the record corresponds to the path of movement traversed by the cutting head of the lathe used to define the master record of which the usual commercially available record is a replica. Thus, in theory, a radial-tracking record player better reproduces the sounds defined in the contours of the walls of the spiral groove of the record.
Virtually all phonograph records now produced, regardless of size, are manufactured to reproduce stereophonic sound. In the cutting of the masters from which the records are reproduced, the cutting tool of the master cutting lathe moves in the cutting head only normal to the master disc (to produce variations in groove depth) and from side-to-side radially of the master disc (to produce local variations in the contour of the groove sidewalls defining the actual audio information); the overall spiral pattern of the groove is generated in the master disc by controlled movement of the lathe cutting head radially of the master disc's axis of rotation.
Thus, to optimally reproduce the sounds recorded in a phonograph record, a record player should limit the motions of the pickup stylus to only those motions which are experienced by the cutting tool used to cut the master disc. Also, the stylus should be mounted in the record player so that it can accommodate these limited motions without any variation in the force with which the stylus engages the record groove. The present record player accomplishes this optimum result significantly better than is the case of record players according to my prior patent, and also better than is the case in other radial-tracking record players now commercially available.
Radial-tracking record players are now commercially available and are marketed in the United States and elsewhere under the tradenames Bang & Olufsen and Rabco, among others. All of these record players mount the stylus and cartridge on the end of an elongate tone arm which is hinged at its other end for rotation of the arm at least in a plane perpendicular to the plane of rotation of a record engaged by the stylus. This is done to enable the stylus and cartridge to move vertically to follow warpage which is common in mass-produced phonograph records. Such hinging of the tone arm enables the stylus to have a freedom of motion not permitted to the cutting tool in the manufacture of the master disc; to at least this extent, these other radial-tracking record players depart from the optimum tracking characteristics described above. The present record player does not afford this additional mode of motion to the stylus and cartridge. The other radial-tracking record players mentioned above suffer from additional disadvantages which are overcome in the present record player.